re-write scale-hsla filter to work in doubles, allowing proper clamping at the right time - refs #1954

include/mapnik/image_filter.hpp

@@ -504,41 +504,46 @@ void apply_filter(Src & src, scale_hsla const& transform)
                 uint8_t & g = get_color(src_it[x], green_t());
                 uint8_t & b = get_color(src_it[x], blue_t());
                 uint8_t & a = get_color(src_it[x], alpha_t());
+                double r2 = static_cast<double>(r)/255.0;
+                double g2 = static_cast<double>(g)/255.0;
+                double b2 = static_cast<double>(b)/255.0;
                 double a2 = static_cast<double>(a)/255.0;
-                double a1 = a2;
-                bool alpha_modified = false;
-                if (set_alpha && a2 > 0.01)
+                // demultiply
+                if (a2 <= 0.0)
+                {
+                    r = g = b = 0;
+                    continue;
+                }
+                else
+                {
+                    r2 /= a2;
+                    g2 /= a2;
+                    b2 /= a2;
+                }
+                if (set_alpha)
                 {
                     a2 = transform.a0 + (a2 * (transform.a1 - transform.a0));
                     if (a2 <= 0)
                     {
-                        a = 0;
+                        r = g = b = a = 0;
+                        continue;
+                    }
+                    else if (a2 > 1)
+                    {
+                        a2 = 1;
+                        a = 255;
                     }
                     else
                     {
-                        a = static_cast<unsigned>(std::floor((a2 * 255.0) +.5));
-                        if (a > 255) a = 255;
+                        a = static_cast<uint8_t>(std::floor((a2 * 255.0) +.5));
                     }
-                    alpha_modified = true;
                 }
-                if (tinting && a > 1)
+                if (tinting)
                 {
                     double h;
                     double s;
                     double l;
-                    // demultiply
-                    if (a1 <= 0.0)
-                    {
-                        r = g = b = 0;
-                        continue;
-                    }
-                    else if (a1 < 1)
-                    {
-                        r /= a1;
-                        g /= a1;
-                        b /= a1;
-                    }
-                    rgb2hsl(r,g,b,h,s,l);
+                    rgb2hsl(r2,g2,b2,h,s,l);
                     double h2 = transform.h0 + (h * (transform.h1 - transform.h0));
                     double s2 = transform.s0 + (s * (transform.s1 - transform.s0));
                     double l2 = transform.l0 + (l * (transform.l1 - transform.l0));
@@ -548,35 +553,19 @@ void apply_filter(Src & src, scale_hsla const& transform)
                     else if (s2 < 0) { s2 = 0; }
                     if (l2 > 1) { l2 = 1; }
                     else if (l2 < 0) { l2 = 0; }
-                    hsl2rgb(h2,s2,l2,r,g,b);
-                    // premultiply
-                    // we only work with premultiplied source,
-                    // thus all color values must be <= alpha
-                    r *= a2;
-                    g *= a2;
-                    b *= a2;
-                }
-                else if (alpha_modified)
-                {
-                    // demultiply
-                    if (a1 <= 0.0)
-                    {
-                        r = g = b = 0;
-                        continue;
-                    }
-                    else if (a1 < 1)
-                    {
-                        r /= a1;
-                        g /= a1;
-                        b /= a1;
-                    }
-                    // premultiply
-                    // we only work with premultiplied source,
-                    // thus all color values must be <= alpha
-                    r *= a2;
-                    g *= a2;
-                    b *= a2;
+                    hsl2rgb(h2,s2,l2,r2,g2,b2);
                 }
+                // premultiply
+                r2 *= a2;
+                g2 *= a2;
+                b2 *= a2;
+                r = static_cast<uint8_t>(std::floor((r2*255.0)+.5));
+                g = static_cast<uint8_t>(std::floor((g2*255.0)+.5));
+                b = static_cast<uint8_t>(std::floor((b2*255.0)+.5));
+                // all color values must be <= alpha
+                if (r>a) r=a;
+                if (g>a) g=a;
+                if (b>a) b=a;
             }
         }
     }

include/mapnik/util/hsl.hpp

@@ -27,11 +27,8 @@
 
 namespace mapnik {
 
-static inline void rgb2hsl(unsigned char red, unsigned char green, unsigned char blue,
-             double & h, double & s, double & l) {
-    double r = red/255.0;
-    double g = green/255.0;
-    double b = blue/255.0;
+inline void rgb2hsl(double r, double g, double b,
+                    double & h, double & s, double & l) {
     double max = std::max(r,std::max(g,b));
     double min = std::min(r,std::min(g,b));
     double delta = max - min;
@@ -47,10 +44,10 @@ static inline void rgb2hsl(unsigned char red, unsigned char green, unsigned char
 }
 
 // http://www.w3.org/TR/css3-color/#hsl-color
-inline double hue_to_rgb( double m1, double m2, double h)
+inline double hue_to_rgb(double m1, double m2, double h)
 {
     if (h < 0.0) h = h + 1.0;
-    else if (h > 1) h = h - 1.0;
+    else if (h > 1.0) h = h - 1.0;
     if (h * 6 < 1.0)
         return m1 + (m2 - m1) * h * 6.0;
     if (h * 2 < 1.0)
@@ -60,16 +57,16 @@ inline double hue_to_rgb( double m1, double m2, double h)
     return m1;
 }
 
-static inline void hsl2rgb(double h, double s, double l,
-             unsigned char & r, unsigned char & g, unsigned char & b) {
+inline void hsl2rgb(double h, double s, double l,
+                    double & r, double & g, double & b) {
     if (!s) {
-        r = g = b = static_cast<unsigned char>(std::floor((l * 255.0)+.5));
+        r = g = b = l;
     }
-    double m2 = (l <= 0.5) ? l * (s + 1) : l + s - l * s;
-    double m1 = l * 2 - m2;
-    r = static_cast<unsigned char>(std::floor((hue_to_rgb(m1, m2, h + 1.0/3.0) * 255.0)+.5));
-    g = static_cast<unsigned char>(std::floor((hue_to_rgb(m1, m2, h) * 255.0)+.5));
-    b = static_cast<unsigned char>(std::floor((hue_to_rgb(m1, m2, h - 1.0/3.0) * 255.0)+.5));
+    double m2 = (l <= 0.5) ? l * (s + 1.0) : l + s - l * s;
+    double m1 = l * 2.0 - m2;
+    r = hue_to_rgb(m1, m2, h + 1.0/3.0);
+    g = hue_to_rgb(m1, m2, h);
+    b = hue_to_rgb(m1, m2, h - 1.0/3.0);
 }
 
 }